Bio-materials Project on an ACL Attachment
Transcript of Bio-materials Project on an ACL Attachment
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ACL AttachmentReplacing Conventional Interference Screws with a Clamp inAnterior Cruciate Ligament (ACL) Reconstruction to Increase
the Creep Resistance of Synthetic Ligaments
March 11, 2011
Meagan Higgins
Amy LautenbachStacy PatchAlex Stanley
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Outline
Background: Current Technology
Material Science and Mechanics
Proposed Solution Test Methods and Procedure
Results
Discussion Recommendations
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Background: CurrentTechnology
Most frequently studied limb in orthopaedic research
ACL provides stability and function of the knee
3 types of ACL Reconstructions
Autografts Allografts
Synthetic
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Background: CurrentTechnology
Interference screws
Endo-button and spiked washer (Smith & Nephew)
Femoral cross pins
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Material Science andMechanics
Ligaments under physiologic loading exhibit nonlinear, viscoelasticbehavior
Further loading recruits more ligament fiber bundles
Viscoelastic Polymers When subjected to applied stress, entropy decreases (less
“disordered”) permanent elongation due to unwinding of the polymer chains
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Material Science andMechanics
Stress relaxation is directly related tostrain
Stress Relaxation in ACL graftsreduces graft forces from the initiallevel set at surgery
Creep represents the non-linearincrease in deformation over timewhen the stress is constant orsubjected to cyclically repetitivestress
Non-linear viscoelasticity indicates time dependent mechanical behavior Principles relate creep and stress relaxation of biological materials
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Material Science andMechanics
Hysteresis: Energy dissipation
When a viscoelastic materialis loaded and unloaded, theunloading curve will notfollow the loading curve
The difference between thetwo curves => amount ofenergy that is dissipated
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Material Science andMechanics
Kevlar
(Aramid Fiber)
Carbon Fiber
TensileStrength (KSI)
464 348
FlexuralStrength (KSI)
363 319
Elongation (%Strain)
1-1.3% 1.8-2%
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Problem Statement/ ProposedSolution
Problem Statement: The elongation due to creepfound in synthetic ACLs prevents the ligamentfrom providing sufficient long-term stability and
makes the ligament more likely to fail. Proposed Solution: If we use an attachment that
better distributes the force exerted by the body
onto the ligament across the entire area of theligament, there will be less stress and wear oncertain fibers which will make it able to lastlonger.
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Proposed Solution
Screw Clamp
C u r r e n
t
: P r o p o s e d :
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Test Method/Procedure
Perform a stress relaxation test on siliconesamples embedded with Kevlar or Carbonfiber braids
DoE: 2 Factors, 2 Levels
Factors: Attachment method, Fiber Material
Levels: Clamp/screw, Kevlar/carbon fiber
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Performing the Test
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Graphing the Results
1. Kevlar; Clamp2. Kevlar; Screw3. Carbon Fiber; Screw4. Carbon Fiber; Clamp
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More Graphs
1. Carbon Fiber; Clamp2. Carbon Fiber; Screw3. Kevlar; Clamp4. Kevlar; Screw
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Discussion/Conclusions
Unable to calculate stress relaxation
Observations show clamp holds higher loadsfor more time
No consistency of kevlar versus carbon fiber